Purpose Built Moto turns the Sportster into a dual sport

Harley Sportster dual-sport conversion by Purpose Built Moto
Custom motorcycles don’t always need to be practical… unless, of course, you need a purpose built machine that can handle a two week adventure ride across Australia. In that case, you’d want something like this tough Harley-Davidson Sportster.

It’s the work of Tom Gilroy, at the aptly named Purpose Built Moto on Australia’s Gold Coast. Purpose Built teamed up with production company Electric Bubble to film an upcoming moto film, Wide of the Mark. Tom needed a ride—so he built this.

Harley Sportster dual-sport conversion by Purpose Built Moto
With a rigorous filming schedule that would see a team of six riders ride the Great Ocean Road and on to Tasmania, each bike had a rigorous task ahead of it. Tom describes the riding as: “long range touring, mountain twisties, off-road logging tracks, tight single track trails, beach riding, and the occasional jump when the mood strikes.”

So what was Tom’s plan for transforming the 2006-model Harley-Davidson Sportster into a pukka dual sport? “I started with shedding weight, and some beefed up suspension,” he says.

Harley Sportster dual-sport conversion by Purpose Built Moto
He stripped the Sporty down to its bones, then tossed the front end in favor of a 2015 Triumph Tiger setup. A set of 14.5” K-Tech Razor shocks was installed out back. The result was an instant suspension improvement, more ground clearance and a bonus weight saving.

Tom took the Triumph’s twin front brakes across too, matching them to a pair of discs from Free Spirits. The front wheel was swapped for a 19” unit, and the Sportster rear hub re-laced to a 17” alloy rim, with a custom-built brake caliper mount.

Harley Sportster dual-sport conversion by Purpose Built Moto
Another major upgrade came via a new aluminum swing arm. Not only is it lighter, but it helped jack the rear up too. This Harley now has about 210 mm of clearance, fully loaded—just 60 mm shy of a Husqvarna 701 Enduro.

Tom’s tire choice for the trip was pretty practical: Mitas E-10 knobbies. “I was super impressed by them,” he says. “Grippy in soft off-road conditions and not noisy or lumpy on road.”

“The only problem I had was in soft sand where the knobby tread pattern and weight of the sportster would simply dig the rear wheel a trench. That’s to be expected when you build a dirt bike out of an American highway pig though!”

Harley Sportster dual-sport conversion by Purpose Built Moto
With only 5,000 kilometers on the clock, the Sportster’s motor was still pretty fresh. So Tom left the internals alone, and upgraded it with a Lectron carb and a two-into one stainless steel exhaust. Then he installed a chain conversion kit, giving him freedom to fiddle with ratios.

But it’s that unique intake that really caught our eye. “I needed an air box,” Tom explains. “No way on earth would I take an adventure bike out with the air box hanging out the side in the weather and dust.”

Harley Sportster dual-sport conversion by Purpose Built Moto
Tom had relocated the bike’s ignition coil, so there was a perfect filter-sized gap up front now. DNA Filters made a custom filter, then Tom fabricated a metal box with a Perspex cover, and stainless steel manifold to link it to the carb.

It inhibits airflow a bit, but the bike still makes 64 hp on a dyno. But the mod ultimately worked; while other riders had constant issues with clogged filters, the Sporty needed just one clean during the trip, and even managed some deep-water crossings.

There’s a lot of practical consideration in the Sportster’s tail section too. Tom needed something that would look sharp but also create packing space, so he shaped a tracker-style tailpiece, and covered it with a sort of exo-skeleton. It includes mounting points for a bag rack and a sissy bar, and there’s a set of LED lights embedded underneath.

Harley Sportster dual-sport conversion by Purpose Built Moto
A simple cable latch releases the nubuck-covered seat, revealing even more storage. There’s enough space in there to stash a small tent and a tool kit.

Up front is the stock XL1200C sportster tank. “The choice of tank was aesthetic,” says Tom, “but also functional, giving me a range of about 330 km (205 miles) per fill.”

Other custom additions include a custom-made rear fender and license plate arrangement at the back, and two-step front fender. The upper bit was hand-shaped from aluminum, but the bottom half was made from a spare fender that was lying around the workshop. And according to Tom, it works.

Harley Sportster dual-sport conversion by Purpose Built Moto
Trick little details abound on this dual-Sporty. Tom built a substantial bash plate, and a set of fork guards with additional lighting built in. There’s a custom-built number board higher up, housing a powerful LED headlight.

Just behind it is a set of ProTaper tracker bars on lengthened risers, dressed up with Purpose Built Moto switches. High-end levers from ISR add useful levels of two-finger feel, and a pair of lever guards protects them.

Harley Sportster dual-sport conversion by Purpose Built Moto
Tom was big on ergonomics when he built up the Harley, so he tweaked the foot pegs as well. They now sit just in front of the swing arm pivot, so that the rider triangle is comfy in both sitting and standing scenarios.

They’re mounted up via custom-made stainless steel cages to work around the Harley’s engine cases, and linked to the shifter and brake with custom linkages. A little extra space ‘inside’ the right hand cage gave Tom an idea—so he wedged an air compressor in there.

“Come off the beach with 18 PSI in the tires,” he explains, “leave the bike running and hit the compressor, and you can ride away on bitumen at 30 PSI, no worries. It came in handy more than a few times during our trip, and is always readily accessible.”

Harley Sportster dual-sport conversion by Purpose Built Moto
Tom reckons that he stripped about 30 kg off the bike in total. He admits that it’s still a handful, but it’s a lot more manageable than before, and having 180 mm of front wheel travel doesn’t hurt either.

But more importantly, since he was building the bike for no one but himself, it gave him a chance to go wild on ideas. He even opted for a special finish on the exhaust; a combination of bead blasting, cleaning and heat-treating for a consistent matte gold finish.

“The finished product is a blend of styles,” Tom says, “perfectly suited to what I think a Sportster scrambler should look like. Tracker styling, but with some completely functional mods that make it a manageable, and enjoyable ride off road.”

Harley Sportster dual-sport conversion by Purpose Built Moto
“It proved itself time and time again on the Wide of the Mark film trip, handling just about any terrain. The only time I really struggled was in really soft sand, but that could be put down to my skills as a rider too.”

“Building a bike like this has taught me a lot—and riding it for two weeks straight as soon as I finished it, taught me even more.”

For a video document of this build—and Tom’s other fine creations—check out the Purpose Built Moto YouTube channel.

Purpose Built Moto | Facebook | Instagram | Images by Akin Moto | Wide Of The Mark Facebook

Harley Sportster dual-sport conversion by Purpose Built Moto